Such a method or system is used in particular in the case of load feeders such as for example motor starters. Switching devices for load feeders are used in switching systems for example, which are normally fused against short circuits and overloading at several levels (feeder, distributor, load). In such a case the state of the motor starter is characterized for example by the switching device controller, a contactor controller for instance, by the feedback relating to the state of the controlled switching device and by the report on the state of the at least one protective device that is arranged upstream thereof, which can be a circuit breaker for example.
The problem resides in the fact that, as a result of the typical configuration within the switch cabinet, wiring outlay is required for these signals, as several wiring lines, (typically six), are required for each feeder, either direct to a controller such as for example a programmable logic controller (PLC), or to a communications switch that is connected to the PLC via a communications interface such as for example a field bus system or a point-to-point interface. Even when communications systems are used to conserve wiring, the protective device must still be connected via wiring, as this wiring ensures that an auxiliary switch on the protective device transmits the report relating to the state of the protective device. However, an auxiliary switch on a circuit breaker does not recognize the lack of power supplied by the mains voltage. As a result of the high wiring outlay, these traditional solutions are not only costly in terms of time and money, but can also constitute a possible wiring error source.